Computers and computer networks are indispensable in modern society. We use computers and computer networks for everything from communication to record storage. Because of the incredible need for computer resources, there is a constant trend toward packaging more and more hardware into less space.
A backplane is a circuit board into which other circuit boards or cards are plugged to provide additional resources or functionality. The backplane provides common resources for the boards or cards it supports. The motherboard in a personal computer may be referred to as a backplane.
A card cage is the central part of the computer where various Printed Circuit Boards (PCBs) are plugged into a centralized backplane. The card cage typically encloses the backplane and card guides for assisting with the connection of cards or other PCBs to the backplane. The backplane houses all of the mating connectors for the installed cards. Many card cages conform to the Compact Peripheral Component Interconnect (CPCI) standard or the Versa Modular Eurocard (VME) standard.
Industry standard VME/CPCI card cages are all basically of the same design. The CPCI card cages can be deployed to support cards being interfaced with one or both sides of the backplane. Obviously, the card cage is larger and more complicated if it supports cards connected to both the front and back sides of the backplane.
A typical CPCI card cage has four front aluminum extrusions that must be fixed in place on the front side of the backplane. Aluminum Extrusions are required for CPCI and VME card cages due to the complex Printed Circuit Board plastic levers and screws that must interface into them. The four card cage extrusions are secured with screws at both ends to the card cage walls. This requires eight total screws that are small and difficult to handle.
Plastic card guides are then added one at a time or in clusters. The plastic card guides guide cards or PCBs that are being connected to the backplane. The card guides also physically support the cards or PCBs after installation. The card guides are, in turn, supported on the card cage extrusions.
On the backside of the card cage, the backplane is attached to the extrusions by numerous M2.5 screws. The M2.5 screws are very small metric screws that are also very difficult to handle.
Also at the rear of the backplane, a rear portion of the card cage can be constructed to support card and PCBs that are plugged into the rear side of the backplane. When Expansion PC Boards (short PC Boards) are to be connected to the rear of the backplane, two rear card cage aluminum extrusions are fixed in place within the backside of the card cage. The two extrusions are screwed to both sides of the card cage wall with four additional screws total. If full-depth PC Boards are to be connected to the backside of the backplane, then four rear card cage extrusions are used. Again, these extrusions are secured in place against the card cage wall with eight screws, one at each end of each extrusion.
Once the rear extrusions are in place, rear plastic card guides are then added one at a time or in clusters. As before, the plastic card guides guide the cards or PCBs that are being connected to the backplane. The card guides also physically support the cards or PCBs after installation. The card guides are, in turn, supported on the card cage extrusions.
In order to repair and replace the backplane, the entire rear card cage must be disassembled. This requires undoing the assembly steps described above in reverse order, right down to removing all of the small screws. This is a tedious process. Moreover, if one drops a screw to the bottom of the card cage or into another component, such as the power supply, etc., then the repair can become extremely difficult.